1. Technical Field
This disclosure relates to biocompatible materials and, more particularly, to biocompatible composite materials such as filaments and sheets. The composite includes a core of a block copolymer initiated with polyalkylene oxide and at least one shell joined to the core, the shell being formed of a block copolymer. The block copolymers have one block made predominantly of hard phase forming monomers and another block made from randomly copolymerized soft phase forming monomers.
2. Background of Related Art
Bioabsorbable materials are known in the art for a variety of uses, particularly those uses in which the bioabsorbable material is implanted within a living organism for medical purposes. The term "bioabsorbable" is used to describe a material capable of being broken down into smaller constituents which can be metabolized and/or excreted by a living organism. Hydrolysis is one mechanism by which many bioabsorbable materials are broken down following implantation within a living organism. Such materials are useful for temporarily holding tissues in a desired position during healing, and being absorbed by the organism after a period of time.
Various bioabsorbable materials and medical devices made therefrom are known in the art. See, e.g., U.S. Pat. Nos. 2,668,162; 2,703,316; 2,758,987; 3,225,766; 3,297,033; 3,422,181; 3,531,561; 3,565,077; 3,565,869; 3,620,218; 3,626,948; 3,636,956; 3,736,646; 3,772,420; 3,773,919; 3,792,010; 3,797,499; 3,839,297; 3,867,190; 3,878,284; 3,982,543; 4,047,533; 4,052,988; 4,060,089; 4,137,921; 4,157,437; 4,234,775; 4,237,920; 4,300,565; 4,429,080; 4,441,496; 4,523,591; 4,546,152; 4,559,945; 4,643,191; 4,646,741; 4,653,497; and, 4,741,337; U.K. Patent No. 779,291; D. K. Gilding et al., "Biodegradable polymers for use in surgery--polyglycolide/poly(lactic acid) homo- and copolymers: 1", Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.), Biocompatibility of Clinical Implant Materials Vol. II, ch. 9: "Biodegradable Polymers" (1981).
Fiber-reinforced compositions used for surgical implants have been described in U.S. Pat. Nos. 4,279,249; 4,550,449; 4,539,931; 4,743,257; 5,080,665. The fiber-reinforcements in these compositions provide increased strength and rigidity as may be required for bone repair, but render these compositions unsuitable where flexibility is required.
U.S. Pat. No. 5,403,347 discloses block copolymers having one of the blocks made from hard phase forming monomers such as glycolide and lactide and another of the blocks made from random copolymers of soft phase forming monomers such as 1,4-dioxane-2-one and 1,3-dioxane-2-one and caprolactone.
U.S. Pat. No. 5,522,841 discloses block copolymers initiated with a polyalkylene oxide. The block copolymers have one block made predominantly of hard phase forming monomers and another block made from randomly copolymerized soft phase forming monomers.
It would be desirable to provide an implantable composite having a bioabsorption rate which varies over time and which is suitable for use in making a variety of medical devices, including those in which flexibility is a desirable characteristic.